1. Field of the Invention
The present invention relates to a radio frequency identification (RFID) system and communication method thereof. More particularly, the present invention relates to an RFID system having an RFID reader and an RFID tag, the RFID system preventing a recognition error of a signal transmitted from an RFID tag, and a communication method thereof.
2. Description of the Related Art
Radio frequency identification (RFID) is a radio frequency recognition technology which identifies an object at a distance by using a radio frequency ranging from MHz to GHz. In RFID, a frequency band is wide, several types of frequencies can be used, and different frequencies can be utilized according to the requirements of particular applications.
RFID has been acknowledged as a key technology for optimizing supply chain management (SCM) technology among existing technologies. In other words, all information with regard to identification, position movement tracking, and profile management of an object can be generated and processed by using RFID technology in an SCM network. In addition, RFID is the technology closest to realizing a ubiquitous network among existing various technologies. As a result, its importance has increased.
In RFID in an ultra high frequency (UHF) band, an RFID tag can be recognized at a distance of approximately 8.4 m in a wireless environment. Such an RFID tag contains a unique identification number (UID). In other words, the RFID tag is attached to an object and stores the UID of the object. An RFID reader identifies the UID of the RFID tag via wireless communication and can read additional information about the object stored in a storage space of the RFID tag.
RFID systems in a UHF band, in comparison with conventional wireless communication systems, are characterized in that the power of a signal transmitted to an RFID tag from an RFID reader is large (e.g. 30 dBm) and the response power of a signal transmitted to the RFID reader from the RFID tag is very small (e.g. −60 dBm). As a result, the RFID reader may not exactly recognize a signal transmitted by the RFID tag.
The RFID tag operates under the power of a radio frequency (RF) electromagnetic field transmitted by the RFID reader. Accordingly, the operation of the RFID tag is constrained by the RF electromagnetic field transmitted by the RFID reader. Thus, a shadow region, in which the RF electromagnetic field does not extend to, may exist. This may lead to reading errors/failure of an RFID tag.
The above-discussed problem is the most serious problem that exists as an obstacle to the commercialization of RFID systems. In other words, when a tag cannot be recognized when goods are delivered from a store or a warehouse, the primary reason for installing the RFID system, i.e. quick and easy identification, cannot be realized. Thus, a technology is necessary that prevents a response error, which causes a user to identify the occurrence of an unrecognized RFID tag.